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Question on under throttle - good or bad?

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Old 11-21-2017, 05:33 PM
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Default Question on under throttle - good or bad?

Don't check my math, but I have to use numbers to highlight the question.

For automatic or CVT transmission.

If I'm cruising at 50 mph with 30% throttle (whatever rpm that is). I approach a 8% decline. At 30% throttle, the car goes faster to 75 mph. So that's not safe.

If I reduce the throttle to 25%, the car still goes fast at 65%.

If I let go of the throttle and be at idle. The car will slow down to 40 mph, 30 mph, 20 mph, etc.

So maybe I should reduce the throttle down to 15%, so the car continue at 50 mph doing downhill. Is this good for the engine to be "under throttle?"

A co-worker said that's not a good idea. Either be on the gas, or let it go. If you are coasting, adjust throttle as necessary until you reach optimal engine load. Under throttle causes excessive transmission wear, when it's not necessary. Experts.., educated me.
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Old 11-21-2017, 05:37 PM
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Default Re: Question on under throttle - good or bad?

use cruise control
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Old 11-21-2017, 05:39 PM
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Default Re: Question on under throttle - good or bad?

:looksatOP'slocation:

Don't you spend the majority of your time idling in traffic? Ask your coworker how much load is on the engine when it is throttled to the point it's not making any power.

75mph is too fast and not safe

Speeding Through Texas: 85 MPH Highway Opens - ABC News
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Old 11-21-2017, 05:49 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by signalpuke View Post
:looksatOP'slocation:

Don't you spend the majority of your time idling in traffic? Ask your coworker how much load is on the engine when it is throttled to the point it's not making any power.

75mph is too fast and not safe

Speeding Through Texas: 85 MPH Highway Opens - ABC News

It was just an example to set up the question. If you want a real example, then, going south in I5 by the grapevine, heading to socal. I could be going down 95mph in a turn. If I continue to gas, I may hit 105 mph. If I let go of the gas, guys behind me goes WTF. Or I can tap my brakes, and guys behind me goes postal. Ok, the easy answer is to go a lower gear. But the Ody does not shift into 5th gear. When you are on 6th, you can only drop it to 4th. This goes back to when Honda AT only have 5 gears.

But I don't want this example to distract from the question at hand, on under throttling the engine.
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Old 11-21-2017, 05:56 PM
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Default Re: Question on under throttle - good or bad?

'Under throttling' is WOT, no?
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Old 11-21-2017, 07:45 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by GoLowDrew View Post
It was just an example to set up the question. If you want a real example, then, going south in I5 by the grapevine, heading to socal. I could be going down 95mph in a turn. If I continue to gas, I may hit 105 mph. If I let go of the gas, guys behind me goes WTF. Or I can tap my brakes, and guys behind me goes postal. Ok, the easy answer is to go a lower gear. But the Ody does not shift into 5th gear. When you are on 6th, you can only drop it to 4th. This goes back to when Honda AT only have 5 gears.

But I don't want this example to distract from the question at hand, on under throttling the engine.
Isn't this all the same as engine braking? IE letting the gearing slow the vehicle down?
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Old 11-21-2017, 08:30 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by Caoboy View Post
Isn't this all the same as engine braking? IE letting the gearing slow the vehicle down?
I don't think so as doesn't the ecu fuel cut with 0 throttle and anything above 2000 rpm?

But his example is 15% throttle so it would keep minimal gas to be semi engine braking while running gas.... Not quite full engine braking.

Thus the idea it's under throttling with light gas and negative load. Instead of no gas and negative load.
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Old 11-21-2017, 09:50 PM
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Default Re: Question on under throttle - good or bad?

The answer is find new co-workers
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Old 11-22-2017, 04:01 AM
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Default Re: Question on under throttle - good or bad?

So a more lightly loaded transmission suffers more wear than a more heavily loaded transmission!? I would love to hear a good engineering or scientific explanation for why that would occur, but I suspect that your co-worker either didn't articulate his point very well or doesn't know what he is talking about.


Originally Posted by 328FTW View Post
The answer is find new co-workers
MIATA is always the answer.
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Old 11-22-2017, 03:29 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by TomCat39 View Post
I don't think so as doesn't the ecu fuel cut with 0 throttle and anything above 2000 rpm?

But his example is 15% throttle so it would keep minimal gas to be semi engine braking while running gas.... Not quite full engine braking.

Thus the idea it's under throttling with light gas and negative load. Instead of no gas and negative load.
Yes, thanks for the clarification. Exactly what I'm asking. It's not engine braking.
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Old 11-22-2017, 03:37 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by tjbizzo View Post
So a more lightly loaded transmission suffers more wear than a more heavily loaded transmission!? I would love to hear a good engineering or scientific explanation for why that would occur, but I suspect that your co-worker either didn't articulate his point very well or doesn't know what he is talking about.

It's probably me, in using GLD examples.

Anyhow, I choose Automatic transmission and CVT because these transmission naturally do slip. And not talking about transmission load.

Let me try another (GLD Example).

You know how some people say it's a bad idea to redline the engine in N, because there is no load. It's actually doing more harm because the pistons are just slapping around as fast as then can. Instead of driving redline at WOT, and the engine is actually "working" in stress. Working in stress is better than slapping around.

So my question is sort of the same thing.

Full engine braking is working stress. WOT is working stress. So what about in-between? So the engine is not at stress with throttle, but there's the engine braking stress countering it.
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Old 11-22-2017, 03:38 PM
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Default Re: Question on under throttle - good or bad?

Or is this just another episode of GLD's Madness???
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Old 11-22-2017, 05:59 PM
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Default Re: Question on under throttle - good or bad?

I suspect it may be your GLD madness.

Are you maintaining a constant speed with the light throttle?

If so, then there is no negative load as you require a certain amount of throttle to maintain the speed. Releasing throttle slows. So, this condition I believe would just be considered light load, light throttle. Nothing wrong with that as far as I can tell.

If on the other hand you are gaining speed with no throttle and you give it light throttle, then I could see this being an "under throttle" condition. And I think the result is you just pick up speed even faster than no throttle.
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Old 11-22-2017, 06:20 PM
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Default Re: Question on under throttle - good or bad?

From your example of the redlining at idle being bad due to lack of stress -
what if you are on flat ground and take off from a stop slowly or maintain speed with light throttle? Itís not redline, but itís light stress.
i feel this is exactly the same as coming downhill and controlling speed with light throttle. It reduces the stress, but does not remove it completely as if you were parked and revving.
Seems your coworker wants you to be flooring it or donít even have your foot on the pedal at all.
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Old 11-22-2017, 06:34 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by 4drEF View Post
Seems your coworker wants you to be flooring it or donít even have your foot on the pedal at all.
Yes, that was the start of the discussion. Not the "floor it" part but that same line - that it is "bad" to baby the throttle going down a hill.

(Wow, I think I just nailed it without the GLD confusion...).
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Old 11-22-2017, 06:49 PM
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Default Re: Question on under throttle - good or bad?

I usually put it in B and recharge the battery
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Old 11-24-2017, 06:58 PM
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Default Re: Question on under throttle - good or bad?

Originally Posted by Caoboy View Post
I usually put it in B and recharge the battery
That made me LoL literally. Thanks.
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